<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Flex练习</title>
    <style>
        .boss{
            width: 600px;
            height: 700px;
            border: 1px dotted black;
            margin: auto;
            display: flex;
            flex-wrap: wrap;

            align-content: flex-start;
        }
        .boss>div{
            width: 100px;height: 50px;
            border: 1px solid red;
        }
        .boss>div:nth-child(1){
            border:1px solid #b3d4fc;
        }
        .boss>div:nth-child(10){
            border: 1px solid indigo;
        }
    </style>
</head>
<body>
    <div class="boss">
        <div>1</div>
        <div>2</div>
        <div>3</div>
        <div>4</div>
        <div>5</div>
        <div>6</div>
        <div>7</div>
        <div>8</div>
        <div>9</div>
        <div>10</div>
        <div>11</div>
        <div>12</div>
    </div>
</body>
</html>